Generally, a gas generating composition used in a vehicular safety device contains fuel components and oxidizing agents. For example, phase-stabilized ammonium nitrate is used as an oxidizing agent, and triaminoguanidine nitrate (hereinafter, referred to simply as TAGN) and a combination of TAGN and guanidine nitrate are used as fuel components (see Patent Document 1: U.S. Pat. No. 5,783,773, for example). There is also a composition in which guanidine nitrate/nitroguanidine is used as a fuel component and in which perchlorate is used as a main substance of an oxidizing agent (see Patent Document 2: U.S. Pat. No. 5,780,768, for example). These compositions are to obtain a preferred combustion rate by combining a component having high reactivity, such as TAGN or perchlorate, with an oxidizing agent and a fuel each of which has inherently low reactivity. However, since the amount of heat generated by the combustion of the compositions rises on the other hand, these gas-generating agents are hardly suitable for a gas generator. There is also a compound being used as a fuel and containing oxygen atoms of 25% or more in an atomic weight ratio in the molecule, and is a combination of a metallic oxide and a plural metallic oxide (i.e., an oxide having a plurality of kinds of metallic components) (see Patent Document 3: Japanese Published Unexamined Patent Application No. 2000-86375, for example). Although the combustion temperature is designed to be low in this composition, the number of gas-generating moles is unsatisfactory because the metallic oxides are used as oxidizing agents. If the number of moles of a gas generated necessary to inflate an air bag is intended to be secured, the amount of gas-generating agents to be used will increase, and, as a result, the amount of heat generated by the combustion of the gas generating agents will increase. In other words, since a large amount of coolant is needed in the gas generator using these compositions, it is difficult to achieve a reduction in size and weight of the gas generator.
A molded article of a gas generating agent that can exhibit a high combustion performance even if its heat value is controlled to be low is shown to solve the above-mentioned problem (see Patent Document 4: Japanese Published Unexamined Patent Application No. H10-87390, for example). This molded article is produced by molding a gas generating agent to be shaped like a cylindrical tube, and is burnt simultaneously from the outer surface of the gas generating agent and from the inner surface of the through-hole so as to burn the agent with high efficiency, and hence is capable of exhibiting a high combustion performance while restricting the amount of heat generated by its combustion. As a result, this publication (Patent Document 4) asserts that a gas generator can be reduced in size and weight. There are also Patent Document 5 (Japanese Published Unexamined Patent Application No. 2000-239092) and Patent Document 6 (Japanese Published Unexamined Patent Application No. 2000-319086), each disclosing a molded article of a gas generating agent that has a recessed portion on the surface thereof.
Generally, a gas generating agent used in a gas generator for air bags is required to instantaneously inflate and expand an air bag when a collision or a similar accident occurs. In this respect, the gas generator that uses a molded article of a gas generating agent that is disclosed in Patent Document 4 (Japanese Published Unexamined Patent Application No. H10-87390) can exhibit a high combustion performance, and therefore can instantaneously inflate and expand an air bag. However, there is a fear that the air bag will adversely affect passengers because of the inflating shock of the air bag when the air bag is rapidly inflated at the beginning of the expansion thereof. If so, the air bag may be incapable of fulfilling its function as a device used to ensure the safety of vehicle occupants. Therefore, an ideal gas generating agent used in an air-bag gas generator is regarded as gradually inflating an air bag at the beginning of its expansion and then rapidly inflating it. In other words, a gas generating agent by which the pressure in a gas generator varies like the letter S with the passage of time is required as a gas generating agent capable of improving the safety of passengers.